There is conventionally known a friction clutch configured to restrict positions of constituent elements of the friction clutch such as clutch plates and a clutch spring related to rotation of a clutch shaft in an axial direction of the clutch shaft. The friction clutch described in Japanese Laid-Open Patent Application Publication No. 2003-322177, for example, has such a structure.
The friction clutch described in Japanese Laid-Open Patent Application Publication No. 2003-322177 is a multiple-disc automatic centrifugal friction clutch used in a motorcycle. The multiple-disc automatic centrifugal friction clutch includes a clutch shaft (=main shaft), a drive plate (=friction plate), and a driven plate (=clutch plate). Furthermore, the multiple-disc automatic centrifugal friction clutch includes a weight roller (=centrifugal weight) and a pressure plate. The pressure plate and the drive plate can slidably move in an axial direction (=thrust direction) of the clutch shaft. By movement of the pressure plate in the thrust direction, the drive plate and the driven plate are pressed. The weight roller receives a centrifugal force by rotation of the clutch shaft and moves radially outward of the clutch shaft. The centrifugal force of the weight roller is converted into a pressing force in the thrust direction of the pressure plate due to the internal structure of the clutch. The drive plate and the driven plate are pressed by the pressing force of the pressure plate. The drive plate and the driven plate which are pressed transmit a drive force of an engine of the motorcycle to a rear wheel.
Moreover, the multiple-disc automatic centrifugal friction clutch includes a clutch plate spring (=clutch spring) generating the pressing force of the pressure plate. Namely, the clutch plate spring presses the drive plate and the driven plate. Further, the pressurization on the drive plate and the driven plate holds the drive plate and the driven plate at predetermined positions at predetermined intervals. Due to this, the multiple-disc automatic centrifugal friction clutch includes a circlip (retaining ring) for restricting positions of constituent elements of a clutch housing such as the pressure plate, the drive plate, the driven plate, the centrifugal weight, and the clutch plate spring in the axial direction of the clutch shaft. This circlip is fitted into the clutch housing covering up the drive plate and the driven plate included in the clutch. A position at which the circlip is fitted into the clutch housing is one end side of the clutch housing in the axial direction of the clutch shaft. The circlip restricts positions of the constituent elements of the clutch housing such as the plate, the centrifugal weight, and the clutch plate spring related to rotation of the clutch shaft in the axial direction of the clutch shaft by being fitted into the clutch housing. Further, the circlip receives a reaction force to the biasing force of the clutch plate spring and prevents detachment of such plates as the drive plate and the driven plate from the clutch housing by being fitted into the clutch housing.
However, if engine power is to be improved in a motorcycle or the like, it is necessary to ensure transmitting the drive force of the high-power engine. Due to this, the clutch serving as a transmission mechanism transmitting the drive force of the engine is configured, for example, so that the diameters of the plates including the friction plate and the clutch plate are increased so as to correspond to the configuration of the high-power engine. In the clutch having such larger-diameter plates, the diameter of the circlip preventing detachment of such plates as the friction plate and the clutch plate is also made larger.
Nevertheless, the inventor of the present application has discovered from various experiments that the circlip often detaches from the clutch housing in friction clutches including a larger diameter circlip.
The present invention has been devised in view of the foregoing problems, and it is an object of the present invention to prevent a retaining ring (such as a circlip) from detaching from a clutch housing.
The inventor of the present application has exerted utmost efforts as well as conducted studies to attain the foregoing object and has discovered that a main cause for detachment of the circlip is a radially inward deformation of the circlip. Specifically, the inventor has discovered that the shape of the circlip and the load imposed on the circlip play a role in the detachment of the circlip. The circlip typically has a substantially annular shape in which an outer circumferential side of the circlip is fitted into the clutch housing. Consequently, deformation of the circlip tends to occur on the inner circumferential side rather than on the outer circumferential side. This deformation is considered to result from the fact that the circlip has the substantially annular shape and, more particularly, has a so-called C shape with a slit formed in a portion of the circlip.
A C-shaped circlip 85 is shown, for example, in FIGS. 5a and 5b. Circlip 85 has a slit or notched portion 85b. When circlip 85 is fitted into a clutch housing, the diameter of the outer circumference of the circlip is temporarily reduced so as to be smaller than an inner hull of the clutch housing. The diameter of the circlip is reduced, for example, by applying an external compressing force to the circlip so that the terminal ends of circlip 85 come into contact with each other. The circlip fitted into the clutch housing generates an expanding force extending along the circlip diameter (hereinafter, referred to as “extension force”). This extension force enables the inner hull of the clutch housing and the outer circumference of this circlip to contact each other.
Furthermore, similarly to the clutch described in Japanese Laid-Open Patent Application Publication No. 2003-322177, the clutch employing the circlip shown in FIGS. 5a and 5b often includes a clutch spring (clutch plate spring). In this case, similarly to the circlip described in Japanese Laid-Open Patent Application Publication No. 2003-322177, circlip 85 is fitted into the clutch housing, thereby receiving a reaction force to the biasing force of the clutch spring. The reaction force to the biasing force of the clutch spring causes the front and rear terminal end surfaces (FIG. 5a) of the circlip to make contact with the clutch housing. The contact of the circlip 85 with the clutch housing allows the circlip 85 and the clutch housing to generate a frictional force in a portion in which the circlip 85 and the clutch housing contact each other.
Moreover, if the clutch including the circlip 85 is a centrifugal clutch similar to the clutch described in Japanese Laid-Open Patent Application Publication No. 2003-322177, the magnitude of the reaction force to the biasing force of the clutch spring varies according to the change in rotational speed of the clutch shaft. Namely, in the case of the clutch described in Japanese Laid-Open Patent Application Publication No. 2003-322177, for example, the weight roller receives the centrifugal force and moves radially outward relative to the clutch shaft by rotation of the clutch shaft. The centrifugal force of the weight roller is converted into a pressing force in the thrust direction of the pressure plate by the internal structure of the clutch. The drive plate and the driven plate are pressed by the pressing force of the pressure plate. During pressing, the drive plate and the driven plate are forced to separate from each other by mutual resistance forces or the like. Due to this, the clutch includes the clutch plate spring as means for generating the pressing force. If the rotational speed of the clutch shaft is higher, the clutch plate spring needs a greater biasing force for pressing the drive plate and the driven plate. In this way, if the biasing force of the clutch disc spring is of relatively high magnitude, the circlip receives a greater reaction force to the biasing force of the clutch plate spring. If the reaction force to the biasing force of the clutch plate spring is greater, a greater frictional force is generated in the portion of the circlip that contacts the clutch housing.
Further, as the clutch shaft rotates, a centrifugal force is generated at mass points on a circular portion of the circlip. This centrifugal force is greater if the rotational speed of the clutch shaft is higher. This centrifugal force and the extension force of the circlip described previously enable the circlip to make contact with the inner hull of the clutch housing on the outer circumferential side of the circlip.
As stated above, the outer circumferential side of the circlip contacts the inner hull of clutch housing by the extension force which is directed radially outward of the circlip. Further, the circlip receives the reaction force to the biasing force of the clutch spring. The front and rear surfaces (front and rear surfaces in FIG. 5a) of the circlip make contact with the clutch housing due to the reaction force of the clutch housing to the biasing force. Due to this, a frictional force is generated in the portion of the circlip that contacts the clutch housing. However, the frictional force applied to the portion of the circlip that contacts the clutch housing is not uniform on the entire circlip. Namely, the force due to friction with the clutch housing differs in magnitude or the like among the mass points on the circlip. This results from the fact that the shape of the outer circumferential side of the circlip does not completely conform to the shape of the inner hull of the clutch housing. Furthermore, surfaces of the circlip and the clutch housing are not completely flat physically, so that portions in which the clutch housing contacts the circlip may include small spaces therebetween. Besides, during driving of the engine related to actuation of the clutch, the frictional force is considered to change at the respective mass points on the circlip.
If the frictional force changes at the respective mass points on the circlip, the circlip is considered to undergo deformation. However, the outer circumferential side of the circlip can make contact with the inner hull of the clutch housing. Due to this, it is considered that the inner circumferential side of the circlip deforms more easily than the outer circumferential side thereof.